7. PROJECT SUMMARY Background. Echoic memory (EM) is a pre-categorical and passive form of auditory short-term memory. EM is essential for processing sounds that are inherently fleeting yet acquire meaning only in relation other sounds. The neural substrate of echoic memory has not bee identified. It is well-established that the processing of a sound temporarily reduces the responsiveness of auditory cortex to similar sounds (refractoriness or stimulus-specific adaptation: R/SSA). It has been noted that R/SSA fade with similar time- constants as information about past sounds fades from EM. The proposed work will test the hypothesis that the cause for the reduced responsiveness that underlies R/SSA is the neural substrate of EM.